China has warned that it will take strong measures if U.S. House of Representatives Speaker Nancy Pelosi visits Taiwan.
Chinese Foreign Ministry spokesperson Zhao Lijian on Thursday told reporters that such a visit would severely impact Chinese-U.S. relations, following media reports she would go next week.
China considers democratically ruled Taiwan its own territory and the subject is a constant source of friction between Beijing and Washington, especially given strong U.S. military and political support for the island.
The possible visit has not been confirmed by Pelosi's office or Taiwan's government, but some Japanese and Taiwanese media reported it would take place after she visits Japan this weekend.
Lijian told reporters that Beijing firmly opposed all forms of official interactions between the United States and Taiwan, and Washington should cancel the trip.
"If the United States insists on having its own way, China will take strong measures in response to defend national sovereignty and territorial integrity. All possible consequences that arise from this will completely be borne by the U.S. side," he added, without giving details.
In Taipei, Taiwan Foreign Ministry spokesperson Joanne Ou would only say that inviting U.S. officials and dignitaries had always been "an important part" of the ministry's work, and that it would announce any official visits at an appropriate time.
Sunday marks the 43rd anniversary of the United States signing into law the Taiwan Relations Act, which guides ties in the absence of formal diplomatic relations and enshrines a U.S. commitment to provide Taiwan with the means to defend itself.
The last time a House speaker visited Taiwan was in 1997 when Newt Gingrich met then-President Lee Teng-hui.
Pelosi, a long time critic of China, particularly on human rights issues, held a virtual meeting with Taiwan Vice President William Lai in January as he wrapped up a visit to the United States and Honduras.
Pelosi is one of the ruling Democratic Party's most high-profile politicians, and second in the U.S. presidential line of succession after the vice president.
Taiwan has been heartened by continued U.S. support offered by the Biden administration, which has repeatedly talked of its "rock-solid" commitment to the island.
That has strained already poor Sino-U.S. relations.
In March, a delegation of former senior U.S. defence and security officials sent by President Joe Biden visited Taiwan, a strong show of support coming soon after Russia invaded Ukraine.